Avalon Exchange consistently has a good selection of used clothing. it's a bit more expensive than goodwill or the salvation army, but you're stuck looking for needles in the hay stack so to speak-- they've done that work for you.
they also buy clothes on the spot. and while they're picky about what they take, it's still a pretty easy way to make $20 (or you can take store credit instead of cash, which will give you a better return).
overall, it's definitely worth checking out.